In 2000, CDC in collaboration with the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) of the National Institutes of Health (NllI) under Program Announcement #00097 (Uniform Population-Based Approach to Case Ascertainment, Typology, Surveillance, and Research on Childhood Diabetes) established a 5-year research project to assess the burden of diabetes with onset in childhood and adolescence in the U.S. The goals of this project (now called SEARCH for Diabetes in Youth) were to: 1) identify prevalent and incident cases of diabetes among individuals under age 20 years in order to estimate population prevalence and incidence rates;2) develop gold standards for the classification of diabetes type in youth;and 3) describe and compare clinical presentation and characteristics of type 1, type 2, and other types of diabetes. This project builds upon the SEARCH results and expands the preliminary findings from SEARCH to enhance our understanding of the natural history, complications, and risk factors of diabetes mellitus with onset in childhood and adolescence. In particular, data from SEARCH reveal important preliminary findings that warrant further scientific study: --The incidence of diabetes in US youth is higher at all the SEARCH sites and among all age groups than had been expected based on estimates from previous diabetes registries. However, this does not necessarily imply that the incidence has increased. Differences in case definition and in ascertainment methodology, or changes in screening patterns, may partly explain the higher incidence estimated by SEARCH. In order to assess temporal trends, it is necessary to monitor diabetes incidence in youth for a longer period of time using consistent methodology for case ascertainment and classification. --Some subjects not only exhibit the clinical features of type 2 diabetes, but also have positive diabetes autoantibody status (a characteristic of type 1 autoimmune diabetes). This finding demonstrates the limits of the current diabetes classification scheme in youth and the need to better understand the natural history and long-term evolution of diabetes in youth, especially those with features of both type 1 and type 2 diabetes. Additional research will also provide consistency and ensure sustainable and simplified criteria for case ascertainment and classification for surveillance purposes, across centers, across popUlations, and over time. This approach will constitute an essential basis for assembling large numbers of incident cases for additional clinical, epidemiological, health care, or therapeutic research into childhood diabetes.